More particularly, the invention is concerned with an offshore tower structure of the kind comprising a central column to extend upwardly in use from the sea bed to support a platform and carry services such as conductors and risers between the sea bed and the platform, and a structure to support the column, the support structure including at least three legs joined at their apex by a sleeve which in use surrounds and supports the column above the sea bed. Such a structure is herein referred to as an "offshore tower structure of the kind defined."
An example of an offshore tower structure of the kind defined is seen in our British Pat. No. 2136860. In this example, the support structure has both upper and lower sleeves for slidably receiving the column. Assembly of this structure is by sliding one end of the column through both the sleeves and fixing, for example, by introducing grout between the column and sleeves.
Another example of an offshore tower structure of the kind defined is seen in our British Pat. No. 2116237. In this example, the support structure includes bracing to provide additional strength and foundations for the column and legs can be pre-installed on the sea bed.
The present invention offers an alternative assembly technique which is suitable, for example, for occasions where the central column is too large to be lifted by an available crane vessel.